Present air filter controllers used on self-cleaning reverse pulse air filters and dust collectors initiate a cleaning cycle on either a fixed or adjustable time interval. Such operation does not take into account various conditions experienced by such filters or dust collectors, resulting in less than optimum performance.
Self-cleaning air filters and dust collectors of the reverse pulse type, such as that shown in U.S. Letters Pat. No. 4,319,897, the teachings of which are incorporated herein by reference, perform a filter cleaning operation by opening a compressed air valve for a short period of time. The resulting blast of compressed air is normally directed into a venturi or eductor tube to entrain a much larger volume of secondary air and develop the static pressure required to force this air back through the filter in a direction opposite to the normal air flow therethrough. It is normal practice to clean or pulse no more then 10% of the filters at one time. This leads to the use of 4 to 26 valves depending on the air flow capacity or size of the air filter or dust collector. Thus, to perform a cleaning cycle it is necessary to provide a means to turn on each compressed air valve in sequence for a prescribed period of time and with a prescribed time interval between pulses.
Currently available controllers do nothing more than turn valves on and off in sequence. The basic timer-type controller operates either continuously or is initiated on the closure of an adjustable pressure switch. Since the pressure loss across the filters increases continuously over the life of the filters, even the pressure switch controlled timer will revert to continuous cleaning unless the set point is frequently increased. These devices require continuous manual attention to fully utilize the life expectancy of a filter.